LibWeb/CSS: Return GC::Ref from Parser::convert_to_style_declaration()

Author: https://github.com/AtkinsSJ
Commit: 9b06f66571
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3983

Libraries/LibWeb/CSS/Parser/Parser.cpp

@@ -1493,7 +1493,7 @@ void Parser::extract_property(Declaration const& declaration, PropertiesAndCusto
     }
 }
 
-CSSStyleProperties* Parser::convert_to_style_declaration(Vector<Declaration> const& declarations)
+GC::Ref<CSSStyleProperties> Parser::convert_to_style_declaration(Vector<Declaration> const& declarations)
 {
     PropertiesAndCustomProperties properties;
     PropertiesAndCustomProperties& dest = properties;